Material Analysis
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PVC Poor Plasticization (Unmelted Material)
Problem Phenomenon
Unplasticized particles and fish-eyes in products, poor mechanical properties, rough surface; profiles and pipes break when bent.
Cause Analysis
PVC is granular powder/pellets, plasticization depends on shear and gelation degree; low temperature, insufficient shear, excessive external lubrication (slipping) all cause incomplete plasticization; unplasticized particles do not fuse, products are 'solid outside but hollow inside', strength greatly reduced.
Solution
①Increase barrel temperature (especially compression zone) and screw shear; ②Check internal/external lubrication balance, reduce excessive external lubrication; ③Increase back pressure; ④Evaluate the gelation degree of the mixture; ⑤Appropriately reduce screw speed to extend plasticization time.
Key Takeaway
PVC plasticization = the triangle of 'temperature + shear + lubrication balance': under-plasticized products look strong but are actually very brittle; excessive external lubrication is the hidden culprit, gelation degree should be monitored as a process indicator.
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